Polyolefin compositions, method for the production and use thereof

ABSTRACT

Compositions comprising one or more olefin polymers functionalized by at least one functionalization agent chosen from carboxylic acids, their esters, their anhydrides and their metal salts and one or more stabilizing agents comprising one or more sterically hindered phenol groups and at most one ester functional group. Process for their preparation and use of these compositions for compatibilizing olefin polymers with polymers, fillers and metal substrates which are incompatible with olefin polymers.

The present invention relates to stabilized compositions formed offunctionalized polyolefins and in particular stabilized compositionsformed of polyolefins functionalized by carboxylic acid groups, theiresters, their anhydrides or their metal salts. It also relates to aprocess for their preparation and to their use.

Functionalized polyolefins are widely used, in particular as adhesivebetween a polyethylene (PE) layer and a layer of epoxy resin, forexample for the coating of pipes. In practice, all plastics are subjectto oxidation phenomena, commonly described using the terminology “ageingphenomenon”. The most widely used method for slowing down thesephenomena is the addition of antioxidizing or stabilizing agents.

Phenolic antioxidants are used as stabilizing agents for polyethylenes.However, their combination with stabilizing agents of phosphite type isgenerally more effective; see U.S. Pat. No. 4,290,941. A frequently usedcombination is, for example, a blend of pentaerythrityltetrakis(3,5-di-t-butyl-4-hydroxyphenylpropionate) and oftris(2,4-di-t-butylphenyl) phosphite.

The problem which is posed in the case of adhesives stabilized in thisway, based on polyolefins functionalized by acid or anhydride groups,for example maleic-anhydride-functionalized polyethylene, is a long-termloss in adhesion. Furthermore, these compositions are subject to a lossin thermal stability and to an increase in the viscosity in the presenceof moisture (loss in rheological stability), this phenomenon furtherbeing accelerated by an increase in the temperature.

The present invention is targeted at overcoming these disadvantages bynovel compositions formed of functionalized polyolefins exhibitingbetter thermal stability and better rheological stability and givingbetter long-term adhesion.

One aspect of the present invention consequently relates to compositionscomprising one or more olefin polymers functionalized by at least onefunctionalization agent chosen from carboxylic acids, their esters,their anhydrides and their metal salts and one or more stabilizingagents comprising one or more sterically hindered phenol groups and atmost one ester functional group.

These functionalized compositions exhibit better rheological stabilityand give better long-term adhesion.

Furthermore, these compositions are no longer subject to a loss inthermal stability nor to an increase in the viscosity in the presence ofmoisture.

The stabilizing agents comprising one or more sterically hindered phenolgroups and at most one ester functional group are chosen fromstabilizing agents comprising one or more sterically hindered phenolgroups which comprise an ester functional group and from stabilizingagents comprising one or more sterically hindered phenol groups which donot comprise an ester functional group.

The term “ester functional group” is understood to denote, for thepurposes of the present invention, the ester functional group derivedfrom the carboxylic acid functional group within the conventionalmeaning of organic chemistry (R—CO—O—R′).

Mention may be made, among stabilizing agents comprising one or moresterically hindered phenol groups which comprise an ester functionalgroup, of, for example, stearylβ-(3,5-di-t-butyl-4-hydroxy-phenyl)propionate.

Mention may be made, among stabilizing agents comprising one or moresterically hindered phenol groups which do not comprise an ester group,of, for example, 1,1,3-tris(2-methyl-4-hydroxy-5-t-butylphenyl)butane,2,2′-isobutylidenebis(4,6-dimethylphenol),2,2′-methylenebis(6-t-butyl-4-methylphenol),2,6-bis(α-methylbenzyl)-4-methylphenol,4,4′-thiobis-(6-t-butyl-m-cresol),2,2′-methylenebis(4-methyl-6-nonylphenol), diisobutylnonylphenol, tris(3, 5-di-t-butyl-4-hydroxybenzyl) isocyanurate,1,3,5-tris-(4-t-butyl-3-hydroxy-2,6-dimethylbenzyl)-1,3,5-tri-azine-2,4,6-(lH,3H,5H)-trione,1,3,5-trimethyl-2,4,6-tris(3,5-di-t-butyl-4-hydroxybenzyl)benzene andtheir mixtures.

Preferably, at least one of the stabilizing agents does not comprise anester functional group. In a particularly preferred way, at least one ofthe stabilizing agents is 1,3,5-trimethyl-2,4,6-tris-(3,5-di-t-butyl-4-hydroxybenzyl)benzene (Irganox® 1330). In a veryparticularly preferred way, the compositions according to the inventioncomprise1,3,5-trimethyl-2,4,6-tris(3,5-di-t-butyl-4-hydroxybenzyl)benzene assole stabilizing agent.

The amounts of stabilizing agent employed in the compositions of thepresent invention depend on various factors, for example on the amountof radical initiator used, on the application intended for thecompositions and on the nature of the functionalization agent. Theamount of stabilizing agent is generally between 0.001 and 1% by weight.

Generally, the amount of stabilizing agent is greater than or equal to0.001%, preferably greater than or equal to 0.01%, in a particularlypreferred way greater than or equal to 0.1% by weight.

Generally, the amount of stabilizing agent is less than or equal to 1%,preferably less than or equal to 0.75%, in a particularly preferred wayless than or equal to 0.5% by weight.

The olefin polymers functionalized by functionalization agents chosenfrom carboxylic acids, their esters, their anhydrides and their metalsalts can be obtained by known techniques, for example bycopolymerization or, preferably, by grafting. They are derivatives ofpolymers formed of linear olefins comprising from 2 to 8 carbon atoms,such as ethylene, propylene, 1-butene, 1-pentene, 1-hexene and 1-octene.

The linear olefins preferably comprise from 2 to 6 carbon atoms, moreparticularly from 2 to 4 carbon atoms.

The olefin polymers (polyolefins) can be selected from homopolymers ofthe abovementioned olefins or from copolymers of these olefins, inparticular copolymers of ethylene or of propylene with one or morecomonomers. The constituent comonomers are advantageously chosen fromthe abovedescribed olefins and from diolefins comprising from 4 to 18carbon atoms, such as 4-vinylcyclohexene, dicyclopentadiene, methylene-and ethylidenenorbornene, 1,3-butadiene, isoprene and 1,3-pentadiene.

The polyolefins are preferably chosen from propylene polymers andethylene polymers, in particular ethylene homopolymer, propylenehomopolymer, ethylene copolymers, propylene copolymers, copolymers ofethylene and of propylene, and their mixtures.

The propylene polymers are generally chosen from propylene homopolymersand copolymers with a melt flow index (MFI), measured at 230° C. under aload of 2.16 kg according to ASTM standard D 1238 (1986), of between 0.1and 100 dg/min.

The ethylene polymers are generally chosen from ethylene homopolymersand copolymers exhibiting a standard density of between 915 and 960kg/m³ and a melt flow index (measured at 190° C. under a load of 5 kg)of between 0.1 and 200 dg/min.

Ethylene homopolymers and copolymers are particularly preferred. Theseadvantageously exhibit a standard density of at least 915 kg/M³, inparticular of at least 936 kg/m³. The standard density generally doesnot exceed 960 kg/m³, preferably does not exceed 953 kg/m³. The ethylenehomopolymers and copolymers, in addition, usually exhibit a melt flowindex (measured at 190° C. under a load of 5 kg) of at least 0.1 dg/min,preferably of at least 2 dg/min. The melt flow index generally does notexceed 200 dg/min, more particularly does not exceed 40 dg/min.

The functionalization agent is generally a compound comprising a vinylunsaturation and optionally one or more aromatic nuclei and/or one ormore carbonyl groups. The functionalization agent can be chosen, forexample, from unsaturated mono- or dicarboxylic acids and theirderivatives, unsaturated mono- or dicarboxylic acid anhydrides and theirderivatives, unsaturated mono- or dicarboxylic acid esters and theirderivatives or unsaturated mono- or dicarboxylic acid metal salts andtheir derivatives. The functionalization agents preferably comprise from3 to 20 carbon atoms. Mention may be made, as typical examples, ofacrylic acid, methacrylic acid, maleic acid, fumaric acid, itaconicacid, crotonic acid, citraconic acid, maleic anhydride, itaconicanhydride, crotonic anhydride, citraconic anhydride and their mixtures.Maleic anhydride is very particularly preferred.

In a particularly preferred way, in the compositions according to theinvention, at least one of the olefin polymers functionalized by atleast one functionalization agent chosen from carboxylic acids, theiresters, their anhydrides and their metal salts is an ethylene polymerfunctionalized by maleic anhydride.

In a very particularly preferred way, in the compositions according tothe invention, the only functionalized olefin polymer is an ethylenepolymer functionalized by maleic anhydride.

The maleic anhydride is usually present in the functionalized ethylenepolymer in an amount of 0.001 to 5% by weight, preferably of 0.01 to 3%by weight and in particular of 0.05 to 1% by weight.

The ethylene polymer functionalized with maleic anhydride advantageouslyexhibits a standard density of at least 915 kgt/m³, in particular of atleast 936 kg/m³. The standard density generally does not exceed 960kg/m³, preferably does not exceed 953 kg/m³. In addition, it usuallyexhibits a melt flow index (measured at 190° C. under a load of 5 kg) ofat least 0.1 dg/min, preferably of at least 2 dg/min. The melt flowindex generally does not exceed 50 dg/min, more particularly does notexceed 22 dg/min.

The compositions according to the invention can, in addition, optionallycomprise additives usual for polyolefins in an amount ranging up to 10%by weight, such as additional antioxidizing agents, lubricating agents,fillers, colorants, nucleating agents, UV stabilizers, antiacid agents,such as calcium stearate, agents for modifying the crystallinity, suchas a copolymer of ethylene and of n-butyl or ethyl acrylate, agents fordeactivating metals or antistatic agents.

One embodiment of the present invention provides for the dilution of theabovedescribed compositions in one or more nonfunctionalized olefinpolymers. In the case of nonfunctionalized olefin polymers, they areessentially the compounds mentioned above or their mixtures. Thecomposition can be diluted up to 20 times, that is to say by addingthereto up to 95% by weight of at least one nonfunctionalized olefinpolymer, preferably up to 10 times, that is to say by adding thereto upto 90% by weight of at least one nonfunctionalized olefin polymer, in amore than preferred way up to 5 times, that is to say by adding theretoup to 80% by weight of at least one nonfunctionalized olefin polymer.

The compositions according to the invention can be prepared by anyprocess, such as, in particular, solution processes, the processes beingcarried out in a mixer, for example a Brabender mixer, or the processesbeing carried out in an extruder. Good results are usually obtained ifthe compositions according to the invention are prepared by means of theprocess according to the invention.

The invention also relates to the use of one or more stabilizing agentscomprising one or more sterically hindered phenol groups and at most oneester functional group in the stabilization of olefin polymersfunctionalized by at least one functionalization agent chosen fromcarboxylic acids, their esters, their anhydrides and their metal salts.

The stabilizing agents comprising one or more sterically hindered phenolgroups and at most one ester functional group used in the stabilizationare those identified hereinabove.

The olefin polymers which can be stabilized are those identifiedhereinabove.

The invention also relates to a process for the preparation ofstabilized compositions comprising one or more functionalized olefinpolymers and one or more stabilizing agents, according to which one ormore olefin polymers, one or more functionalization agents, one or moreradical initiators, one or more stabilizing agents comprising one ormore sterically hindered phenol groups and at most one ester functionalgroup, and optionally one or more additives, are melt blended in a screwextruder.

The stabilizing agent comprising one or more sterically hindered phenolgroups and at most one ester functional group which can be introducedinto the extruder are those identified hereinabove.

A preferred case is that where at least one of the stabilizing agentsintroduced into the extruder does not comprise an ester functionalgroup. A particularly preferred case is that where at least one of thestabilizing agents introduced into the extruder is1,3,5-trimethyl-2,4,6-tris(3,5-di-t-butyl-4-hydroxy-benzyl)benzene. Avery particularly preferred case is that where the1,3,5-trimethyl-2,4,6-tris(3,5-di-t-butyl-4-hydroxybenzyl)benzene isintroduced into the extruder as sole stabilizing agent.

The stabilizing agents are usually employed in an amount of between0.001 and 1% by weight, preferably between 0.01 and 0.75% by weight andin a particularly preferred way between 0.1 and 0.5% by weight.

These olefin polymers are those identified hereinabove.

A preferred process is that in which at least one of the olefin polymersintroduced into the extruder is an ethylene polymer exhibiting astandard density of 915 to 960 kg/m³ and a melt flow index, measured at190° C. under a load of 5 kg, of 0.1 to 200 dg/min.

The functionalization agents which can be introduced into the extruderare chosen from carboxylic acids, their esters, their anhydrides andtheir metal salts and are essentially those indicated above.

A preferred alternative form of the process is that where at least oneof the functionalization agents introduced into the extruder is maleicanhydride.

A very particularly preferred alternative form is that where the onlyfunctionalization agent introduced into the extruder is maleicanhydride.

The functionalization agents can be introduced into the extruder eitherin the solid state or in the molten state. In the latter case, it isnecessary to have available an introduction system maintained at atemperature greater than the melting temperature of thefunctionalization agent.

The functionalization agents are generally used in an amount of 0.001 to20% by weight, preferably of 0.05 to 10% by weight and in particular of0.01 to 5% by weight.

The grafting reaction in the process according to the invention takesplace under the effect of a radical initiator. Organic peroxides arepreferably used as radical initiator. Mention may be made, as typicalexamples, of t-butyl cumyl peroxide,1,3-di(2-t-butylperoxyisopropyl)benzene,3,5-bis(t-butylperoxy)-3,5-dimethyl-1,2-dioxolane, di-t-butyl peroxide,2,5-dimethyl-2,5-di(t-butylperoxy)hexane, p-menthane hydroperoxide,pinane hydroperoxide, diisopropylbenzene mono-α-hydroperoxide, cumenehydroperoxide, t-butyl hydroperoxide and their mixtures. The preferredradical initiator is 2,5-dimethyl-2,5-di-(t-butylperoxy)hexane.

The radical initiator is generally employed in the process according tothe invention in an amount sufficient to allow the grafting to becarried out. The amount is usually between 0.0001% and 1%, preferablybetween 0.001 and 0.5%, in a particularly preferred way between 0.01 and0.1% by weight.

The temperature by which the process is carried out is generally greaterthan the melting temperature and lower than the decompositiontemperature of the polyolefin and of the functionalized polyolefin, ifpossible optionally at an optimum temperature for the radical initiator.The process according to the invention generally involves processingtemperatures in the range from 120° C. to 290° C., preferably in therange from 140 to 250° C. and, in a particularly preferred way, in therange from 160 to 220° C.

During the process, it is optionally possible to additionally introduceat any point, for example, up to 10% by weight of conventional additivesfor polyolefins chosen from those mentioned hereinabove.

The process can also provide for the dilution of the composition in oneor more nonfunctionalized olefin polymers. The nonfunctionalized olefinpolymers are essentially the compounds mentioned above or theirmixtures. The composition can be diluted up to 20 times, that is to sayby adding thereto up to 95% by weight of at least one nonfunctionalizedolefin polymer, preferably up to 10 times, that is to say by addingthereto up to 90% by weight of at least one nonfunctionalized olefinpolymer, in a more than preferred way up to 5 times, that is to say byadding thereto up to 80% by weight of at least one nonfunctionalizedolefin polymer.

The dilution of the composition can take place continuously in the screwextruder in which the preparation of the stabilized composition takesplace. It can also take place in a device separated from the saidextruder, for example in a second extruder, optionally after granulationof the stabilized composition.

The order of introduction of the reactants is generally not critical.The functionalization agent, the stabilizing agent and the radicalinitiator can be introduced at the same time or independently in anyorder and optionally portionwise. The stabilizing agent is preferablyintroduced after the functionalization agent and the radical initiator,in a particularly preferred way after the reaction region.

In a very particularly preferred way, the process for the preparation ofstabilized compositions according to the invention comprises thefollowing stages:

a) feeding, under a nitrogen atmosphere, one or more olefin polymers andfrom 0.001 to 20% by weight of functionalization agent into a corotatingtwin-screw extruder equipped with a series of associated blendingelements with skewed threads,

b) feeding from 0.0001 to 1% by weight of a radical initiator,optionally diluted in one or more olefin polymers or optionallyintroduced by spraying,

c) blending one or more molten olefin polymers, the functionalizationagent and the radical initiator in the extruder prepared for a timesufficient to graft at least a portion of the functionalization agentonto the molten olefin polymer(s),

d) feeding into the extruder from 0.001 to 1% by weight of stabilizingagent and optionally one or more other additives, optionally diluted inone or more olefin polymers,

e) devolatilizing the volatile materials by a subsequent stage ofdevolatilization with hot dry air in a decompression region of theextruder,

f) optionally diluting with nonfunctionalized olefin polymers,

g) discharging the final composition.

A screw extruder within the meaning of the present invention comprisesat least the following parts: a feed region, a reaction region and, atits outlet, a discharge region preceded by a compression region, thelatter forcing the molten mass to pass through the discharge region.

In practice, all the stages can be carried out in a corotating orcounterrotating single- or twin-screw extruder which generallycomprises, in addition to the abovementioned regions, optionally one ormore staged feed devices for the said introduction of the polyolefin orpolyolefins, functionalization agents, radical initiator and/orstabilizing agent, one or more screw elements allowing the propagationof the material to be extruded, one or more heating regions allowing theconstituents to be melted and one or more devolatilization regions. Ifappropriate, the composition can also be diluted in a region allowingthe introduction of nonfunctionalized polyolefin via an appropriate feeddevice. In addition, the discharge region can be followed by agranulation device.

The process according to the invention is advantageously used for thepreparation of the compositions according to the invention.

Finally, an additional aspect provides for the use of the compositionsin accordance with the present invention for compatibilizing olefinpolymers with polymers, fillers and metal substrates which areincompatible with olefin polymers.

Incompatible polymers are, for example, epoxy resins, fluorinated resinsand particularly poly-(vinylidene fluoride), polyamides and polyesters.

The compositions according to the invention are preferably used forcompatibilizing olefin polymers with epoxy resins.

Incompatible fillers are, for example, natural fibres, such as flax,hemp, jute and cellulose, and glass fibres, glass, silica, talc, calciumcarbonate and carbon black. The metal substrates are, for example, steelor aluminium.

Preferred uses of the compositions according to the invention aremultilayer adhesion and the multi-layer coating of steel pipes.

The following examples serve to illustrate the present inventionwithout, however, limiting the scope thereof.

The meanings of the symbols employed, the units expressing thequantities mentioned and the methods for measuring these quantities areexplained hereinbelow.

Standard density (SD) of the polyolefin expressed in kg/m³, measuredaccording to ISO standard 1183 (1987).

The melt flow index of the polyolefin (MI₅) is determined at 190° C.under a load of 5 kg, 8/2 mm die, according to ISO standard 1133 (1991).

The grafted content of MA is evaluated by IR spectroscopy. Two films areprepared per sample and analysed directly after pressing and then afterdegassing for 1 h at 120° C. under vacuum in order to remove, ifnecessary, the residual free anhydride. The MA level, measured by IR, isexpressed by the ratio of the absorbance of the carbonyl (1785 cm⁻¹) tothe absorbance at 3610 cm7′characteristic of PE. The acid level isexpressed by the ratio of the absorbance at 1715 cm⁻¹ to the absorbanceat 3610 cm⁻¹. The values obtained are converted to % by weight ofgrafted maleic anhydride by making use of a relationship based on atitrimetric calibration. The free maleic anhydride is detected by thecharacteristic bands at 895, 840 and/or 700 cm⁻¹.

The thermal stability is determined by measuring the induction periodunder oxygen at 210° C. according to ASTM standard D 3895 (1992).

The peel strength was evaluated on 5×15 cm three-layer plates. 5×15×3 mmmetal plates are sandblasted for at most 24 h before coating. Anapproximately 100 μm layer of epoxy primer is applied at 200° C. byelectrostatic powdering. The plate is placed in a mould base preheatedto 200° C. A film of the adhesive composition of the exampleshereinbelow with a thickness of approximately 250 μm is applied and thenan Eltex® GTB 201 PE plate with a thickness of approximately 3 mm. Thepeel strength is then measured according to DIN standard 30670 (1991).

In the examples which follow, the base resin is the Eltex® A 4090 P HDPEpolyethylene resin with an MI₅ of 29 dg/min and a standard density of952 kg/m³. The maleic anhydride (MA) is milled. The peroxide is2,5-dimethyl-2,5-di(t-butylperoxy)hexane (DBPH-Peroxyd Chemie). Aftergrafting, the products are dried in an oven at 80° C. under vacuum for16 h in order to remove the free MA.

EXAMPLE 1

A sample of Eltex® A 4090 P polyethylene functionalized with maleicanhydride in the absence of any stabilizing agent, which comprises 1% ofgrafted maleic anhydride and which exhibits a melt flow index of 6.6dg/min before and after hydrolysis, is mixed on a Brabender mixer at180° C., 50 rotations per minute, for 6 min in the presence of 3 g/kg ofthe stabilizing agent1,3,5-trimethyl-2,4,6-tris(3,5-di-t-butyl-4-hydroxybenzyl)benzene(stabilizing agent A).

Half of the sample is hydrolysed in the presence of steam for 7 days at100° C. and then dried under vacuum overnight at 85° C.

Measurements of the melt flow index and of the thermal stability werecarried out on the samples as such or on the samples after hydrolysis.The results of these measurements are summarized in Table I.

EXAMPLE 2 (COMPARATIVE)

The procedure is the same as in Example 1 except that the stabilizingagent employed is the stabilizing agent pentaerythrityltetrakis(3,5-di-t-butyl-4-hydroxyphenylpropionate) (stabilizing agentB).

The results of the measurements of melt flow index and of thermalstability are summarized in Table I.

TABLE I Thermal Thermal stability stability MI₅ without MI₅ afterwithout after hydrolysis, hydrolysis, hydrolysis, hydrolysis,Composition dg/min dg/min min min Example 1 7.1 6.4 18.8 15.4 Example 27.2 0.1 18 0 (comparative)

It is apparent from the analysis of the results that the compositionsaccording to the invention exhibit a constant long-term melt flow indexand thermal stability.

EXAMPLE 3

A mixture of linear high density polyethylene (HDPE), sold under thetradename Eltex® A 4090 P, and of maleic anhydride in the solid state,at a content of 0.4% by weight, is fed to a Krupp Werner & PfleidererZSK58 corotating twin-screw extruder.

The extruder is arranged so that it successively comprises the followingregions:

(1) Main feed region

(2) Heating region provided with a feed orifice

(3) Reaction region provided with a feed orifice

(4) Degassing region for discharging the volatile materials

(5) Compression region

(6) Discharge region.

The HDPE, blended with the maleic anhydride, is fed to the main feedregion under a stream of nitrogen. The peroxide is fed to the mainhopper in the feed region at a content of 0.045% by weight in the formof a masterbatch with the HDPE. The stabilizing agent1,3,5-trimethyl-2,4,6-tris(3,5-t-butyl-4-hydroxy-phenyl)benzene(stabilizing agent A) is added in the region 3 at a content of 0.3% byweight in an HDPE/stabilizing agent masterbatch concentrated 10 fold.

The other operating conditions are as follows:

Temperature profile: 210° C.

Throughput of 180 kg/h

Screw speed: 300 revolutions per minute.

The functionalized polyethylene comprises 0.5% by weight of maleicanhydride and exhibits a melt flow index MI₅ of 20 dg/min and a thermalstability of 20 min.

The peel strength was evaluated as described hereinabove on the sampleas such or on the sample aged for 15 days at 80° C. in water. Theresults of the peel strengths, measured at 23° C. and 80° C., arepresented in Table II hereinbelow.

EXAMPLE 4 (COMPARATIVE)

The procedure is carried out in the way described in Example 3, exceptthat the stabilizing agent employed is the stabilizing agentpentaerythrityl tetrakis(3,5-di-t-butyl-4-hydroxyphenylpropionate)(stabilizing agent B), all the other conditions being identical.

The results of the peel strengths, measured at 23° C. and 80° C., arepresented in Table II hereinbelow.

TABLE II Peel strength at 23° C. Peel strength at 80° C. (N/50 mm) (N/50mm) 23° C. and aged 80° C. and aged for 15 d at 80° C. for 15 d at 80°C. Composition 23° C. in water 80° C. in water Example 3 1150 1150 562429 Example 4 1200 195 550 100 (comparative)

It may be observed from the analysis of these results that thecompositions according to the invention give better long-term adhesion.

What is claimed is:
 1. A composition comprising one or more ethylenepolymers having one or more functional groups selected from the groupconsisting of a carboxylic acid, an ester of a carboxylic acid, ananhydride of a carboxylic acid and metal salts thereof, and one or morefirst stabilizing agents having one or more sterically hindered phenolgroups and not more than one ester group, and at least one secondstabilizing agent having one or more sterically hindered phenol groupsand not having an ester functional group.
 2. The composition accordingto claim 1, wherein the total amount of the stabilizing agents isbetween 0.001 and 1% by weight.
 3. The composition according to claim 1,comprising an ethylene polymer comprising a maleic anhydride functionalgroup.
 4. The composition according to claim 3, wherein the maleicanhydride functional group is present in the ethylene polymer in anamount of 0.001 to 5% by weight.
 5. The composition according to claim3, wherein the ethylene polymer having a maleic anhydride functionalgroup has a standard density of 915 to 960 kg/m³ and a melt flow index,measured at 190° C. under a load of 5 kg, of 0.1 to 50 dg/min.
 6. Thecomposition according to claim 1, further comprising one or more olefinpolymers not having a functional group.
 7. A process for the preparationof a stabilized composition comprising one or more ethylene polymershaving a functional group and one or more stabilizing agents, saidprocess comprising melt blending in an extruder one or more ethylenepolymers, one or more functionalization agents, one or more radicalinitiators, one or more first stabilizing agents having one or moresterically hindered phenol groups and not more than one ester group, andone or more second stabilizing agents having one or more stericallyhindered phenol groups and not having an ester functional group.
 8. Theprocess according to claim 7, wherein at least one of the ethylenepolymers melt blended in the extruder is an ethylene polymer having astandard density of 915 to 960 kg/m³ and a melt flow index, measured at190° C. under a load of 5 kg, of 0.1 to 200 dg/min.
 9. The processaccording to claim 7, wherein at least one of the functionalizationagents melt blended in the extruder is maleic anhydride.
 10. The processaccording to claim 7, wherein the melt blending is carried out at atemperature of between 120° C. and 290° C.
 11. The process according toclaim 7, further comprising: mixing the stabilized composition with oneor more nonfunctionalized olefin polymers.
 12. A stabilized compositionobtained by the process as claimed in claim
 7. 13. The process accordingto claim 7, further comprising: mixing the composition with one or moreolefin polymers that do not comprise a functional group selected fromthe group consisting of a carboxylic acid, an ester of a carboxylicacid, an anhydride of a carboxylic acid, and metal salts thereof. 14.The composition as claimed in claim 1, consisting essentially of one ofmore of the ethylene polymers, the first stabilizing agent and thesecond stabilizing agent.
 15. The process according to claim 7, whereinthe stabilized composition consists essentially of one or more of theethylene polymers, the first stabilizing agent and the secondstabilizing agent.
 16. The composition as claimed in claim 1, whereinthe ethylene polymers are ethylene homopolymers.
 17. The process asclaimed in claim 7, wherein the ethylene polymers are ethylenehomopolymers.